ACCESSORY INSTRUMENTS. 



143 



piece of metal to keep down the tail. Some of the advantages 

 of this little apparatus wiU be hereafter alluded to. 



Phial Holder. — This instrument, the contrivance of Mr. 

 Varley, is represented in elevation by fig. 97, and in section 

 by fig. 98. It consists of a tube of brass about an inch-and- 



Fig. 97. 



Fig.! 



a-half in diameter, and two or more inches in length, having 

 an oval hole cut out at the top, and a smaller tube attached to 

 the lower side, immediately opposite the hole ; within this last 

 slides a stiU smaller tube, provided in its interior with stops 

 like those in the dark chamber, fig. 57 and a curved plate of 

 brass at its top ; it is capable of being moved up and down, 

 but a spiral spring always presses it towards the hole^ in the 

 large tube. The use of this apparatus is obvious ; a smooth 

 wide mouth phial, having chara or other water plants growing 

 in it, is to be introduced into the large tube in the manner 

 represented by fig. 97, the small spring tube having been first 

 pushed down, the phial is then kept firmly in contact with the 

 upper surface of the outer tube, but not so firm but that it 

 may be either turned round or slid in or out. The small 

 outer tube, besides containing the dark chamber, serves^ the 

 purpose of attaching the whole of the apparatus to the stage 

 of the microscope. In order that the phial may move very 

 smoothly, all the parts fitting against it should be lined with 



